1. Field of the Invention
The present invention relates to a storage apparatus and a read error recovery method of the storage apparatus, and more particularly, to a storage apparatus provided with an error recovery procedure (ERP) including a self diagnostic feature used in a hard disk drive and a read error recovery method thereof.
2. Description of the Related Art
Hard disk drives write or read data to or from a disk surface using magnetic changes in the disk surface. A transducer head is positioned at a predetermined position of a track in which data is recorded and reads information from the track of the disk rotating at a high speed. There exist situations when errors occur while data is being read using the transducer head, thus various conventional ERPs for recovering errors have been disclosed. For example, U.S. Pat. No. 5,533,031 discloses a method of recovering errors in a recording medium drive using an ERP and a data verification method.
When a hard disk drive reads data from a disk, read errors occur due to defects on a disk or misregistration of a track. Registration means determining an accurate position or adjusting a position based on a given reference.
When such errors occur, an ERP is performed, which include error recovery operations such as changing various parameters and re-reading, in order to increase readability. Generally, data errors are recovered using an error correction code (ECC). In cases of a change in read gain, a change in an off-track, and use of magnetic resistance (MR) device as a read head, an error recovery operation changing a bias value of the MR device is performed.
When reading of data succeeds, by performing error recovery and re-reading, the data is continuously used. However, an error that cannot be recovered even through a plurality of error recovery operations is a fatal error. When data can be rewritten or reassigned to an area other than a current area on a disk, the data is rewritten to another area, and the current area is determined as a non-usable area.
FIG. 1 is a flowchart of a conventional read error recovery method, and FIG. 2 is a diagram showing error recovery operations used in the conventional read error recovery method. The conventional read error recovery method will be described with reference to FIGS. 1 and 2.
As illustrated in FIG. 1, an attempt to read data from a disk is made (S10). Thereafter, it is determined whether the data has been read successfully (S12). If it is determined that the data has been read successfully, normal data is output (S14), and the operation ends.
If it is determined that the data has not been read successfully, that is, if an error occurs during the data reading process, an ERP is performed. In the conventional ERP, a parameter set for each error recovery operation in advance is sequentially applied to re-read the data. Accordingly, a predetermined parameter for a current error recovery step is applied (S16).
More specifically, referring to FIG. 2, first and second error recovery operations are performed in a default mode. In the default mode, reading is re-tried without changing parameters. In a third error recovery operation, an off-track parameter is changed to +15%, that is, an off-track offset is set to 15% in a positive direction.
Next, the current error recovery operation is increased by one (S18). It is determined whether the increased current error recovery operation comes after a predetermined last error recovery operation (S20). If it is determined that the current error recovery operation does not come after the last error recovery operation, the operation goes back to operation S10 to re-try data reading.
If re-reading of the data is successfully performed, the normal data is output, and the ERP ends. However, if re-reading of the data is not successfully performed, a parameter set for the current error recovery operation is applied (S16). For example, if the current error recovery operation is a fourth error recovery operation, the off-track parameter is changed to −15%, that is, the off-track offset is set to 15% in a negative direction.
As described above, when data re-reading is not successful with a predetermined parameter corresponding to a current error recovery operation, a predetermined parameter corresponding to a subsequent error recovery operation is applied to the process of re-reading the data. If data reading is performed successfully in a 30th error recovery operation, normal data can be output and automatically reassigned, that is, recorded in an unused area on the disk.
In the meantime, if data reading is not performed successfully after the last error recovery operation, the error is determined as a fatal error (S22), and the ERP ends.
As described above, in the conventional error recovery method, predetermined error recovery operations are sequentially performed regardless of the characteristics or causes of the errors. Accordingly, it is difficult to recover data errors caused by complex factors with the conventional error recovery method. For example, when there are errors in data that can be recovered using an off-track parameter of +20%, a read gain parameter of +8, and an MR bias parameter of +4, the data cannot be read if the conventional error recovery operations do not include such a combination of parameters.
Meanwhile, in large capacity and high performance hard disks, a track density and a spindle motor's revolutions per minute (RPM) increase. Accordingly, the probability of data being off-track during recording or the probability of the occurrence of an ECC error increases.
Therefore, an improved re-try algorithm for data read errors is desired in order to increase the possibility of successfully reading data from a hard disk.